Scientists have long been fascinated with paradox: why a large part of the Earth is covered by water, while the water itself is less than one percent of the total mass of the planet? Rebecca Martin and Mario Livio of the Scientific Institute for space telescope in Baltimore (USA) conducted a study, which may have been found the cause of the mysterious contradictions.

Previously it was assumed that the Earth was formed in the outer part of the so-called protoplanetary disk of the Solar system rich in water ice, beyond the so-called "the snow line". In this case, it had to be a water world, a kind of Solaris". However, this did not happen. Moreover, experts believe that the water on our planet appeared only because of cometary bombardment. Even oceans small European satellites of Jupiter, contain twice as much water as the earth's sea...

"The snow line" is called the zone of the Solar system lies in the region of the asteroid belt. Radiation from the Sun there are five to six times weaker than near the Ground, and therefore not able to evaporate the water ice from the surface cosmic phone Experts have long believed that up to dispel the protoplanetary cloud "snow line" would be much closer to the Sun - and not even because gases protoplanetary cloud should disperse radiation of the lights, and for the simple reason that at the dawn of his youth Sun warmed by 20-30 percent weaker than in our day. So "line snows" was to be closer to the star than now.

However, Rebecca Martin and her colleagues believe that this line for the whole period of existence of the Solar system was always located at a distance of not more than 1,5-2 astronomical units from the Sun. At that, no Earth, no planets like Mars, Venus and mercury never got beyond "snow line", so in their composition is so little water.

If you follow the standard model of formation of the planets, the 4.5-4.6 billion years ago gas-dust disk around the Sun was completely ionized. In this part of its matter was falling down on the Sun (just as it does in the accretion disk), so the mass of the Sun gradually increased, and that the drive is considerably warmed up. Because of this warming line snows" could be located only at a good distance from the star - up to 1.6 billion kilometers.

However, over time the disk began to dissolve, and the matter was no fall in the Sun, and heating is reduced almost to zero. It promoted "snow line" closer to the Sun. When the protoplanetary cloud is completely resorbed, "the snow line" again shifted to the area of the asteroid belt.

However, at the dawn of the Solar system the Sun shone still too weak to ionize the radiation of the protoplanetary disk. But if he was not fully ionized, ionized gas could not fall on the surface of light, and therefore around him at a distance from 0.1 up to a few astronomical units had to form "dead zone", getting in which the substance could not move on to the Sun.

The accumulation in this area of the substance grew its specific density, which has led to gravitational effects gathers dust material in a protoplanetary education (planetesimals), among whom was our Land. In the process of compression of matter in the "dead zone" extremely hot, which contributed to intensive evaporation of water ice. It was then that the future of the planet has lost the most part of water.

If everything had happened exactly this explains why the composition of water in the chondrites, which, as is, is our planet, does not correspond to the composition of the basic amount of water on it (in particular, it differs in content of isotopes deuterium), but it is identical to the water composition of comets and asteroids.

According to Martin and Livio, in ancient times, the Ground was very dry, like a current of Venus, and the water on her, brought the body, who arrived from space - for example, of a comet.

This is confirmed by the fact that the oldest earth rocks (age 4.3 and 4.4 billion years) contain significant amounts of water, which, according to the employees of the Institute for space telescope, simply could not be on the planet before late cometary bombardment. Since all biological creatures consist mainly of water, it is possible to conclude that life on Earth is a space origin.